The reduction of crosstalk within audio signals is of major interest in a plurality of applications. For example, when reproducing binaural audio signals for a listener using loudspeakers, the audio signals to be heard e.g. in the left ear of the listener are usually also heard in the right ear of the listener. This effect is denoted as crosstalk and can be reduced by adding an inverse filter, also referred to in the art as crosstalk cancellation unit, into the audio reproduction chain configured to filter the audio signals.
Mathematically, the inverse filter for realizing crosstalk cancellation can be expressed as a crosstalk cancellation filter matrix C. The goal of crosstalk cancellation is to choose the crosstalk cancellation filter matrix C, more specifically its elements, in such a way that the result of a matrix multiplication of the crosstalk cancellation filter matrix C with an acoustic transfer function (ATF) matrix H is essentially equal to the identity matrix I, i.e. H*C≈I, where the ATF matrix H is defined by the transfer functions from the loudspeakers to the respective ears of the listener.
Finding an exact crosstalk cancellation solution is not possible and approximations are applied. Because inverse filters are normally unstable, these approximations use a regularization in order to control the gain of the crosstalk cancellation filter and to reduce the dynamic range loss. However, due to ill-conditioning inverse filters are sensitive to errors. In other words, small errors in the reproduction chain can result in large errors at a reproduction point, resulting in a narrow sweet spot and undesired coloration as described in Takeuchi, T. and Nelson, P. A., “Optimal source distribution for binaural synthesis over loudspeakers”, Journal ASA 112(6), 2002.
Audio systems are known in the art that combine crosstalk cancellation units with binauralization units for providing crosstalk free virtual surround sound, i.e. crosstalk free sound perceived by the listener to be produced at virtual loudspeaker positions. However, often such binauralization units introduce unavoidable small errors, which are then amplified by the non-prefect crosstalk cancellation units resulting in more coloration and wrong spatial perception.